This invention relates to a toner for development of electrostatic image to be used in electrophotography, etc., more particularly, a toner for development of electrostatic image improved in fixability without lowering the improved off-set performance, and a method of fixing a toner image employing the same.
Generally speaking, in the dry developing system, a powdery toner for development of electrostatic image charged is attached through electrical attraction onto an electrostatic latent image on a photosensitive member, then transferred onto a paper and fixed by hot rolls, etc.
Accordingly, such toner for development of electrostatic image is demanded to have various properties such as anti-blocking property (toner particles should not be agglomerated), anti-off-set property (toner should not be attached onto hot rolls, etc.) and fixability (toner should be firmly attached to paper). Particularly, recently, the toner for development of electrostatic image has been demanded to have good fixability at lower temperatures.
In the prior art, for improvement of anti-off-set property, it has been proposed that the binder in the toner for development of electrostatic image is constituted of a resin comprising a polymer component with low molecular weight and a polymer component with high molecular weight (see Japanese Unexamined Patent Publications Nos. 158340/1981, 16144/1981 and 202455/1983).
However, although an improvement of anti-off-set property can be surely accomplished by introducing a polymer component with high molecular weight into the toner for development of electrostatic image, if the glass transition point or softening point of the low molecular weight polymer component is lowered in order to realize good fixability at lower temperature without causing lowering of the improved anti-off-set property, anti-blocking property will be lowered.
On the other hand, if the proportion of the polymer component with low molecular weight is increased by decreasing the proportion of the polymer component with high molecular weight in order to realize fixability at lower temperature, anti-off-set property will be worsened.
On the other hand, there is also a proposal, in which the binder is constituted of, for example, a styrene-acrylic acid type polymer, and its molecular weight distribution is made broader without particularly incorporating a polymer component with high molecular weight as described above in this polymer, and moreover, by forming ion bonding of the carboxylic group in the polymer with metal atoms by the reaction with a metal compound to form a crosslinked structure through metal atoms, thus consequently realizing improvement of anti-off-set property by effecting formation of substantially high polymer through the crosslinked structure, although having no special polymer component with high molecular weight (see Japanese Unexamined Patent Publications Nos. 110155/1986 and 110156/1986).
However, such toner for development of electrostatic image contains a large amount of a metal compound formulated therein, and therefore the metal compound formulated may exhibit a catalytic action depending on the condition, whereby the resin in the toner for development of electrostatic image may be readily gelled, and therefore there are problems such that it is difficult to determine preparation conditions for obtaining a desired toner for development of electrostatic image by formulation of a metal compound, or that even the preparation conditions can be determined, reproducibility is bad, etc.